The present invention relates to a shock-absorbing mechanism for a power-transmission device or propeller shaft for motor vehicles, and more particularly, to the shock-absorbing mechanism for absorbing an input load acting axially on the propeller shaft upon vehicle collision.
A typical shock-absorbing mechanism for a power-transmission device of this type is disclosed in JP-A 10-250390. This shock-absorbing mechanism is applied to a propeller shaft for motor vehicles, wherein the propeller shaft comprises a first shaft on the transmission side and a second shaft on the driving-wheel side, which are coupled together through a tripod universal joint. A rear end of the first shaft is formed with an outer race of the universal joint, whereas an end of the second shaft on the first-shaft side is formed with an inner shank having a front end arranged through the outer race.
The outer race is formed like a bottomed cylinder, wherein an opening opposite to a bottom wall is covered with an annular member and a boot, and an annular groove is formed in the outside face of the bottom wall. The inner shank is rotatably supported-to a vehicle body through a center bearing, and has a tripod arranged protuberantly at the outer periphery of the front end and positioned by an annular protrusion. The tripod is slidably engaged with three grooves formed in the inner peripheral face of the outer race, thus configuring the universal joint. The center bearing has a stepped cylindrical support member arranged at the outer periphery. An annular elastic body is integrated with the outer peripheral face of the support member.
Thus, if a collision occurs so that an impact is applied to the vehicle from the front to move the first shaft backward, the outer race is moved backward together with the first shaft to have the bottom wall colliding with the inner shank and the tripod.
Further backward movement of the outer race causes the inner shank to intensely push the bottom wall of the outer race, which is finally broken along the annular groove to allow penetration of the inner shank. At that time, colliding with a portion of the bottom wall exterior of the annular groove, the tripod is pushed back by the bottom wall. Then, the annular protrusion of the inner shank for positioning the tripod serves as a stopper to provide a given resistance. By breaking the annular protrusion over the given resistance, the inner shank is moved backward together with the tripod, thus obtaining shock-absorbing operation.